This invention relates generally to tissue fixation and more particularly to tissue fixation in a waveguide with a magnetron generating radio frequency energy therein.
As is well known, pathologists diagnose diseases by examining tissue samples from biopsies or other similar medical procedures. Because it is important that the cells be examined in a state as close to the living state as possible, the tissue samples are typically put through a chemical fixation process in order to stop the cells from degrading. More specifically, the samples are typically immersed in a preserving solution which commonly includes formaldehyde. The solution penetrates the walls of the cells, hardens the cell structure and thereafter prevents or greatly retards further degradation. Subsequently, a pathologist subjects the sample to various tests and examinations for diagnosis.
One significant problem of the above-described fixation process is that it takes a relatively long period of time, such as, for example, eight hours, for the preserving solution to penetrate the cell walls. Accordingly, the fixation process may prevent a relatively fast diagnosis. Also, at least during the early stages of fixation, the cells continue to degrade. This delay may cause the cells to change from their original living state, and, in some cases, may cloud the diagnosis.
In the prior art, it has been found that microwave energy speeds up the penetration of the preserving solution into cells. More specifically, in order to speed up the fixation process, submersed tissue samples have been placed in multimodal microwave ovens. When a multimode oven is used, the specimen is placed in a vial with a formaldehyde solution and then placed within a microwave oven cavity. The microwave oven is then powered on for a period of one to two minutes. For reasons not fully understood but apparently related to the vibration of molecules, the presence of the microwave field greatly increases the rate at which the fixation solution penetrates the cell walls. For example, the microwave field may reduce a typical fixation process from several hours down to about 1 minute.
The method of fixating cells using a multimode microwave oven has presented certain disadvantages. A multimode cavity has wide dispersion of microwave energy. This dispersity results in the specimen being heated in a non-uniform manner, thereby causing the specimen to have hot or cold spots. In some cases, cells in hot spots will be destroyed and cells in cold spots will not become fixated.
In addition, using a multimode microwave oven presents the problem of an inconsistency of results every time the microwave oven is used. A multimode microwave oven has the fields constantly changing throughout the oven. These changes cause a different heat pattern within the specimen each time the specimen is fixated. Inconsistency of fixation causes errors in analysis because the pathologist needs a stable baseline in which to make his diagnosis.
Other problems with a multimode oven include requiring the use of a very high power magnetron. In a multimode cavity, microwave energy is spread over a large area. This dispersion of microwave energy may result in a low concentration of energy being distributed to the specimen. Accordingly, to get a high concentration into the specimen requires a high power microwave energy source.
It has also been observed that when the specimen or sample touches the side of a vial during fixation in a microwave single mode cavity, hot spots develop on the sample at the point where the sample touches the vial. These hot spots could destroy the specimen and cause invalid diagnosis when the specimen is looked at under a microscope.
Also, if there is any moisture on a vial in a single mode microwave cavity, the vial may be subject to cracking when exposed to higher power microwave energy.
Finally, using a microwave oven to fixate cells causes problems with the amount of exposure to the cell. In a typical microwave oven, the cell exposure time that can only be adjusted on a second-to-second basis. During fixation, it is sometimes desirable to expose the cell to a specified length of time accurate to within one-hundredth of a second.